Evening Primrose family (Onagraceae)
Description: During the first year, this plant develops a rosette of basal leaves. During the second year, this biennial plant bolts to become 3-7' tall at maturity, branching above. The stems are light green, angular or terete, and moderately to densely covered with spreading white hairs. Alternate leaves occur along these stems that have ascending blades; they are sessile or short-petiolate. The leaf blades are up to 7" long and 1" across, although they are usually about one-half of the maximum size. The leaves are narrowly lanceolate or elliptic in shape, while their margins are entire (toothless) or slightly dentate. The leaf surfaces are yellowish green or medium green and glabrous to slightly pubescent (usually becoming more glabrous with age). However, during the autumn, the leaves often become reddish in response to cold weather. The upper stems terminate in open panicles of floral spikes that are up to 2½' long and across. In each spike, the sessile flowers bloom gradually from the bottom to the top with flower buds above and developing seed capsules below.
Each flower is about ½" long and across, consisting of 4 white to pink petals, a narrow calyx tube with 4 green to red sepals at its apex, 8 long-exserted stamens, and an inferior ovary with a long-exserted style. The petals are oblanceolate in shape, tapering to narrow clawed bases; they are arranged in a semi-circle above the reproductive organs. The sepals are linear-lanceolate, short-pubescent, and strongly recurved or deflexed (bent downward or away from the petals). The stamens have white filaments and slender yellow anthers. The slender style is white; it has a 4-lobed stigma at its apex. The branches of the inflorescence are light green or reddish green, angular or terete, and short-pubescent. The blooming period occurs from mid-summer to mid-autumn, lasting about 1-2 months. The flowers are replaced by seed capsules that are 6-8 mm. long, fusiform (spindle-shaped), slightly 4-ribbed, and short-pubescent. Each capsule contains a few seeds.
Cultivation: This biennial plant prefers full sunlight and more or less mesic conditions. It tolerates many kinds of soil, include those that contain loam, clay, gravel, or sand.
Range & Habitat: The native Biennial Gaura occurs in most counties of Illinois, where it is occasional to locally common (see Distribution Map). Habitats include mesic prairies, meadows in wooded areas, limestone glades, abandoned fields, gravelly banks along rivers, roadside embankments, areas along railroads, and waste areas. Biennial Gaura prefers disturbed areas where there is reduced competition from other plants, although it is occasionally found in higher quality habitats.
Faunal Associations: The flowers are cross-pollinated by long-tongued bees (especially bumblebees) and nectar-seeking moths, including the Northern Corn Earworm Moth (Heliothis zea). Other insects feed destructively on the foliage, flowers, developing seed capsules, and plant sap of Biennial Gaura. Insects in this latter group include aphids (Macrosiphum gaurae, Macrosiphum pseudorosae), leaf-mining larvae of a Momphid moth (Mompha argentimaculella), gall-forming larvae of a a Momphid moth (Mompha rufocristatella), and larvae of the Primrose Moth (Schinia florida) and Gaura Moth (Schinia gaura). Larvae of the latter two moths feed on the flowers and developing seed capsules. The adults of these two moths often hide near the flowers of Biennial Gaura during the day; they are well-camouflaged because of their pinkish or reddish colors. This plant's relationships with vertebrate animals is currently unavailable.
Photographic Location: The photographs of plants were taken along a railroad in Champaign, Illinois, and at a prairie of Meadowbrook Park in Urbana, Illinois.
Comments: During late summer when this tall plant is in full bloom, its lanky stems and flowering spikes have a tendency to sway with each passing breeze. Biennial Gaura (Gaura biennis) has not received much attention because of its untidy appearance and slightly weedy nature. However, it provides attractive flowers during the hot and dreary month of August, when other plants are usually dormant. Biennial Gaura closely resembles Large-flowered Gaura (Gaura longiflora), except this latter species has short appressed hairs along its stems, rather than long and widely spreading hairs. Large-flowered Gaura has a more western distribution than Biennial Gaura, and it is less common in Illinois. Another species with a more western distribution, Small-flowered Gaura (Gaura parviflora), has more densely pubescent leaves, a less branched inflorescence, and smaller flowers than Biennial Gaura. Small-flowered Gaura is uncommon in Illinois, where it is adventive.